A series of experiments are proposed on isogenic animals (prepared by nuclear transplantation) to test the time-position model of neuronal connectivity in the developing visual system of Xenopus laevis. A principal goal of the program is to correlate the patterns of retinal fibers (as determined by whole mount silver staining) with the development of visuo-tectal projections in tadpoles. We ask whether ordering of tectal connections correlates with the development of a radially organized pattern of fasicles within the retina. The latter become organized into a radial system of bundles because of normal mechanics of retinal growth and a simple principle of fiber following. We plan to study the time of appearance of fibers in the retina, the organization of fibers in the optic nerve and tract and the ordering of fibers and tracts in the diencephalon in normal and experimental situations (e.g., eye rotation, compound eyes, etc.). In addition, we are studying regeneration of optic nerves in tadpoles to determine whether the rules governing optic fiber regeneration are the same as those controlling growth and connectivity of embryonic fibers. These studies are correlated anatomically and physiologically, with biochemical analyses of transmitter synthesis in the developing retina.